Fig. 2-2. Atoms have nuclei and electrons. The nuclei contains positive charges and the

electrons are negatively charged.

Any atom has an equal number of positive charges in its nucleus and negative charges

in its electrons.

The electrons exist at particular levels.

Molecules

• Molecules are formed when atoms are connected to one another.

• These connections are called “bonds” and can be thought of as an attractive force that holds the parts of the molecule together.

• We will talk about ionic bonds, covalent bonds, and hydrogen bonds.

Ions are formed when electrons are transferred.

The charged ions are then

attracted to one another due to their opposite charges. We

see this in Fig. 2-3

Now go to your notes for the explanation of how covalent bonds

are formed.

Fig. 2-4. Here are some examples of

molecules held together by covalent

bonds.

Now we need to ask the question “Where are these shared electrons most likely to be found?” There are

two answers:

Now we need to ask the question “Where are these shared electrons most likely to be found?” There are

two answers:

• The electrons may be uniformly distributed throughout the molecule.

Now we need to ask the question “Where are these shared electrons most likely to be found?” There are

two answers:

• The electrons may be uniformly distributed throughout the molecule.

• The electrons may be more likely found at one end or the other of the molecule.

Now you need to go to your notes to see the consequences of these

two different answers.

Fig. 2-5 shows the most famous of the polar compounds, water.

• Since polar compounds have unlike partial charges, they will attract one another at their unlike charges.

• Remember that an attraction between molecules is a bond?

• This attraction between polar compounds is another type of bond. . . .

These bonds are

called hydrogen bonds and are shown in Fig. 2-6.

Individual hydrogen bonds are very weak, but there are SO MANY OF THEM!!!!!

Here is a brief review of the three types of bonds:

• Covalent: formed by the sharing of electrons. These are the strongest bonds.

• Ionic: formed by the attractions between charged ions resulting from the transfer of electrons. These are intermediate in their strength.

• Hydrogen: attractions between partial charges found in polar covalent compounds.